Chlorine and alkali metal hydroxide, for example, sodium hydroxide and potassium hydroxide, are commercially prepared by the electrolysis of the corresponding alkali metal chloride brines in an electrolytic cell. In one type of cell, where the anode is separated from the cathode by an ion permeable barrier, chlorine is evolved at the anode according to the reaction: EQU 2Cl.sup.- .fwdarw.Cl.sub.2 +2e.sup.-
while hydroxyl ion is produced at the cathode according to EQU 2H.sub.2 O+2e.sup.- .fwdarw.H.sub.2 +2OH.sup.-
which is actually a multi-step reaction in which a hydrogen species is absorbed onto the surface of the cathode and the hydrogen molecule is desorbed therefrom.
The total hydrogen reaction, as a series of postulated adsorption and desorption steps, consumes about 0.8 volts in an alkaline solution, such that if the cathode in a chlorine cell is depolarized with oxygen instead of being allowed to evolve hydrogen, a savings of about 1.2 volts is possible, since the oxygen reduction reaction can theoretically generate 0.4 V. The cathodes previously developed for utilization of oxygen as a depolarizer were characterized by a structure of a thin sandwich of a microporous separator of plastic combined with a catalyzed layer, wetproofed with, e.g., polytetrafluoroethylene, and pressed onto a wire screen current collector. In the prior art depolarized cathodes, oxygen is fed into the catalyst zone through the microporous backing. Such cathodes work. However, they suffered from various deficiencies, including separation or delamination of the various layers and flooding of the microporous layer.